The subject invention relates to the problem of providing a robust, compact characterization of a block of printed text which will distinguish the block of text from other such blocks. More particularly, it relates to the problem of providing an image-based characterization of a printed address block which can be incorporated into a digital postal indicium.
Postage metering systems account for postage and other values such as parcel delivery service charges and tax stamps, and print indicia representative of such values as proof of payment. To protect against counterfeiting of indicia modern digital postage metering systems use encryption technology. The postage value and other information relating to an indicium are preferably digitally signed, or otherwise cryptographically authenticated, and the information and signature are incorporated into the digital postal indicium.
Digital postal indicia using encryption technologies are extremely secure. In general, without knowledge of the proper encryption keys, it is essentially impossible to produce a counterfeit digital indicium. However, digital indicia are subject, as are all postal indicia, to “rubber-stamp” duplication or reply attack where a valid indicium is scanned and reproduced on multiple mail pieces. To prevent such “rubber-stamp” duplication it is known to incorporate information from the address block of the mail piece into the postal indicium. Because space on an envelope is limited, typically only a small portion of the information in the address block will be incorporated into the indicium.
In FIG. 1, typical prior art mailing system 10 includes address printer controller 12, address printer 14, postage meter 16, and indicia printer 20. Address printer controller 12 receives address information from a data processing system (not shown), generates a bitmap, and controls address printer 12 to print address block A, representative of the address, on envelope F. Meter 16 receives postage information, and other information, from the data processing system. Meter 16 also receives characterizing information descriptive of block A from address printer controller 12. The information received can be either text-based or image-based. Text-based information is descriptive of the words or characters making up to the address, (e.g., ASCII code) while image-based information is descriptive of the actual printed image bits of pixels in the address block. Meter 16 combines the characterizing information with the postage value and other information, typically digitally signs the combination, generates a bitmap representative of an indicium including the digitally signature and controls indicia printer 20 to print indicium I on envelope E. When the mail piece is received by a postal service, the address block can be scanned again, and the information regenerated from the scanned address block compared to information recovered from indicium I; thus tying indicium I to the particular mail piece. (Note that since the indicium is cryptographically linked to the address on the mail piece, printer 20 need not be a secure printer; but can be a general purpose printer which can be controlled by other devices for other uses.) Commonly assigned, provisional application System And Method For Mail Destination Address Information Encoding Protection And Recovery In Postal Payment”, Ser. No. 60/386,868 discloses a system similar to that of the FIG. 1 using text-based characterizations of the address block.
While useful for its intended purpose, system of FIG. 1 and similarly systems still have problems. It has proven difficult to reliably recover textual information from address blocks during the validation process using available optical character recognition (OCR) techniques. Attempts to increase the robustness of text-based systems by incorporation of additional information and/or the use of error correcting codes has resulted in undesirable increases in indicia size and computational complexity. Thus, it is an object of the present invention to provide a method and system for providing descriptive information which will substantially uniquely identify a block of text in a robust and compact manner. (By “robust and compact” herein is meant information which is small enough in quantity to be incorporated into postal indicia yet will identify a text block, and distinguish among text blocks, with sufficient reliability to deter “rubber stamp” despite errors introduced by the printing and/or scanning processes.)